This invention relates to a highly precise electronic timepiece which comprises a highly precise time reference signal supply source and more particularly to an electronic timepiece comprising a time set mechanism which is capable of easily, reliably and precisely setting time to a time reference signal and which can provide a highly reliable time holding faculty.
In electronic timepieces, it has been the common practice to use a frequency reference signal generator, for example, a crystal oscillator using a crystal oscillating element for the purpose of obtaining a time unit signal. Such electronic timepiece provides accuracy which is significantly higher than that of a mechanical timepiece and an electrical timepiece which make use of a mechanical oscillator in general and a synchronous motor using a commercial electric source in general. A highly precise electronic timepiece has already been proposed to provide accuracy on the order of 0.03 to 0.3 second a day. Such highly precise timepiece can exhibit given property only when it is provided with a time correction mechanism which is reliable in operation. Because, the correct time is displayed by precisely setting the time to be displayed, that is, by precisely setting the kept time of the timepiece per se to a standard time being observed.
In a prior art time set mechanism, "hour" and "minute" are corrected by operating a operating mechanism such as a winding crown, while "second" is corrected by temporarily stopping the stepwise movement of a second hand or by using a return mechanism such as a heart-shaped cam. The return mechanism causes the second hand to return to a "0 second" position and to start again when the second hand coincides with the standard time.
Such mechanical operation, however, results in at least 0.2 second slowness in average when a user corrects the display time with respect to the standard time depending on the user's skill. In addition, various kinds of errors are produced dependent on whether the user pushes the correction button only one time or he keeps up his button push operation. The value of these errors becomes far larger than the error inherent to the timepiece per se and eventually arrived at several seconds.